Color drenching to me says some color not white but as far as the 50% cut it will still look different they are on different planes .. For Greige in all its variations is a dated color but I do not see the greige in that paint it looks fresh. I would not bother changing it , you will alos notice your lighting will have an effect too many variables to worrry about just all one color if drenching is what you want

When I want to lighten a color I buy one sample of color and one sample with no colorant added. I use a syringe to measure out various shades.

Color A 1 cc Color B 3 cc 25%

Color A 1 cc Color B 2 cc 33%

Color A 2 cc Color B 2 cc 50%

Color A 2 cc Color B 1 cc 66%

Color A 3 cc Color B 1 cc 75%

I play until I get just the right shade differential that I am looking for.

I will do this when I have 2 similar colors that are just not quite hitting the sweet spot (blue green - want something between one that feels too green and one that feels too blue)

I often use the same color or a slightly lighter color on the ceiling as on the walls. You do have to take into consideration that the ceiling is usually painted in a flat paint vs a matte or eggshell paint. Make sure you are testing the correct sheen.

The one thing I don't do, unless I am doing a full white on white design, is color drench the trim. Trim always transitions to other rooms, so unless I am using that color for all my trim it causes breaks that I don't care for. I don't like to have to repaint trim. If I use a nice, neutral white for all trim I can change wall color without having to repaint the trim.